Method and apparatus for producing halftone dot images



Filed March l5 1;,22

` I Y n M L V I [A s" .1R l A ,n c vf. fa 1 N; Ilf

` MBTHQD AND APPARATUS FOR PRODUCIG HLFTONE DOT IMAGES Patented Nov. 24, i925.

My invention relates to a method and an apparatus for producing halt-tone dot images.

In carrying out my invention, I employ a graded density screen either in a camera in place of the usual diaphragm or I may dispense with both the lens and diaphragm and use the graded density screen in a. dgilldr-U bOX eceeaiunctleiltvffli. -..tieltrt9i1e-seteeitsiiice of light, a transpareiic'y and a sensitive surface.

In a method heretofore employed tor producing half-tone dot images a camera was JOHN ivi. HAMMOND, o1!" PHILADELPHIA,frnNNsYLvNIA.'i

apli/inaction AND APPARATUs 'Percezione-cms, HALFTNE Dori" IMAGES.

PAr-aiiigeriri'ca; I

.i-vi-. Tf1- if 2"; tone screen therein land `provided with .at graded density screen inlplacelzof the. usual diaphragm. I A y i u 2 is a longitudinal, secl @erik-bm.imnga-gededifd i'none'endth'ereofff"" m Figs. 3, l and 5 are views of diii'erent types oi graded density screens.

The same reference characters are used to indicate similar parts in the several views.

Referring to Fig. l, the reference numeral l indicates a camera and 2 a copy hoard. The camera is provided with the usual lenses' 3 and-a graded density screen 4r which takes the place of the usual diaphragm. Towards the rear end of the camera is provided a half-tone screen in front of a sensitive surface 6.

I have found that with the above apparatus a dot image of the subject Whether direct from nature or a copy can be secured with the elimination of the calculations ot' employed having the half-tone sereenlocated-` the relation of size of diaphragm and screen therein withprovisimmjiistmentin ,au c'-fd an ce h size of...tlie diaphiragnn the focalexteiision and the character ot ruling of the screen employed. These adjustments required exact calculations and expert workmanship to produce satisfac- -tory results.

ly my invention, I am enabled to simplify or eliminate these calculations and ad justnicnts altogether, for, both in the camera and the dark-box the location ot' the screen may be fixed. Moreover, with the dark-box l am enabled to produce Without the use oiIV a lens a half-tone dot image from a continuous tone original more simply than with, and in a` fraction oi' the time required ior, the camera and with a small incandescent light in place of the usual arc lights.

Looking at the invention 'from a theoretical viewpoint the image formed by the aperlure ol thc screen is essentially a. pin-hole" image of the diaphragm and accordingly there is formed behind each screen aperture an optical wedge which spreads in accord alice with well-known sensitoinetiic laws iii the sensitive .medium iii accordance with the intensity of the light falling upon the aperture.

For a full understanding of my invention reference is had to the accompanying drawings, in which- Fig. l is a View partly .in elevation and partly in section ot' a camera having a haltdistance, while the time ot exposure must be calculated upon only one variable, which is the density of the transparency, a relatively easy quantity to measure.

Referring to Fig. 2, the reference numeral T indicates a simple dark-box having a g graded density screen in one end thereot and having at the rear al half-tone screen 5, transparency S and sensitized medium (3.'

The transparency 8 may be either a negative o' a. positive. In View ot' the fact that no lenses are employed in this apparatus, a relatively weak source of light, such as a small incandescent bulb 9, may be employed.

'lhe graded density screen may be o t' anyv desired shape, pattern or kind of gadation according to the character of dot desired.

rlhus, in Fig` 3 is illustrated a. graded deusity screen in which the gradation is from clear at the center 10 to black at the edge 1l, whereas in Fig. 4f is illustrated a gradation from clear at the edge l2 to black at the center 13, and in Fig. 5 is illust-ated a graded density aperture having the shape ot' a Maltese cross, the gradation varying l'roiii clear at the center 14 to dark at the edges 15.

Having now described my invention, what I claim as new and desire to secure by Letv ters Patent is:

l. The method of producing a half-tone dot: image which comprises passing the light from the object to a sensitized medium graded from the center outward at one end of said Chamberand a half-tone screen' near the other end of the Chamber,` said chamber being adapted to receive a sensitized medium behind said half-tone screen.

4. Apparatus for producing halfltone dot images, comprising a chamber for excluding the light, a graded density screen graded from the center outward at onenend of said chamber, a half-tone screen near the opposite end of said chamber, Said chamber being adapted to receive 'a' sensitized medium behind said screen. e

Signed at lVashington, in

Columbial theDistrict o1. y this 14th dayof March A. "D.

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` @Toi-IN ai.' HMMOND, 

